On a cold Tuesday in a Pankow side street, the electrician fitting a heat pump to the back wall of a 1930s terrace pauses over a form he did not have to fill in two years ago. Below the unit’s rating plate — nine kilowatts of thermal output, a compressor that will pull several kilowatts of electricity from the grid on the coldest mornings — there is now a box to tick. The machine must be registered as a steuerbare Verbrauchseinrichtung, a “controllable consumption device”, with the local grid operator. From that moment, on paper at least, the warmth of the house is something the network can turn down.
This is the quiet collision at the centre of Germany’s heating transition, and Berlin is where it is most visible. The country has decided, in law, that the future of domestic warmth runs through electricity. The wires that would carry it were laid for a different century.
The law that picked a winner
The amended Gebäudeenergiegesetz — the Building Energy Act, known to almost everyone as the Heizungsgesetz, the “heating law” — came into force on 1 January 2024 after one of the most bruising legislative fights of the last coalition. Its core demand is deceptively simple: every newly installed heating system must, in principle, draw at least 65 per cent of its energy from renewable sources. In designated new-build areas the rule bit immediately. For existing buildings, the obligation is tied to each municipality’s heat plan — large cities such as Berlin must publish theirs by mid-2026, smaller ones by mid-2028.
The law does not name the heat pump. It does not have to. For a free-standing house with no district-heating pipe at the kerb, the electric heat pump is very often the only technology that clears the 65-per-cent bar without heroics. The federal government attached a number to the ambition: 500,000 new heat pumps installed every year from 2024 onward, a figure meant to signal to manufacturers that the demand was real and the factories worth building.
The factories were built. The demand did not arrive. According to the Bundesverband Wärmepumpe (BWP), the German heat-pump association, sales in 2024 fell by roughly 46 per cent to around 193,000 units — down from a record of about 356,000 the year before, and well under half the political target. The reasons were ordinary and human: the public argument over the law had frightened households, municipal heat plans were not yet written, and few people could explain which subsidy applied to them. The BWP and the heating-industry body BDH spent the year asking, in effect, for the politics to stop frightening the customers.
What the grid can quietly do
The same first of January 2024 brought a second, far less debated change. A revised version of section 14a of the Energiewirtschaftsgesetz (EnWG), the Energy Industry Act, took effect, and with it a new bargain between households and the people who run the low-voltage network. Any new controllable device drawing more than 4.2 kilowatts — a heat pump, a wallbox for an electric car, certain battery and air-conditioning systems — must accept that the grid operator may, in a moment of threatened overload, temporarily reduce the power it draws.
The German verb that has attached itself to this is dimmen — to dim, as one dims a light. The Bundesnetzagentur, the federal network agency that wrote the rule, was careful about the limits. The operator may throttle, not switch off at will; a guaranteed floor of 4.2 kilowatts per connection must remain available, enough to keep a house from going cold; and the heaviest intervention is bounded. In exchange, the household pays a reduced grid fee. It is, on the agency’s own framing, a safety valve rather than a routine instrument — a way to let many more heat pumps and chargers connect to a given street before the cables have to be dug up and replaced.
That last point is the one that matters. The 65-per-cent rule and the 500,000 target both assume that the electricity will simply be there, at the kerb, on the coldest evening of the year. Section 14a is the admission, written into federal law, that on some streets it may not be — and that the cheapest way to manage the gap, for now, is to spread the load rather than to rebuild the network all at once.
The law decided the future of warmth runs through electricity. The wires that would carry it were laid for a different century.
On § 14a EnWG and the Gebäudeenergiegesetz
The cold-evening arithmetic
The physics is unforgiving in a way the politics is not. A heat pump works hardest exactly when everyone else’s does — in the still, dark hours of a January cold snap, when outdoor temperatures fall, efficiencies drop, and electric resistance back-up heaters quietly switch in. Layer onto that street a row of electric cars all plugged in after the evening commute, and a low-voltage transformer sized in the 1970s for lights, a television and a fridge begins to look distinctly modest.
None of this is a Berlin problem alone; it is a feature of dense, old European cities everywhere. But Berlin makes the tension legible because its building stock is so uniform. The Gründerzeit tenements and the inter-war estates were wired for a modesty of demand that no longer holds, and the courtyards and pavements above the cables are crowded, listed, and expensive to open. Replacing a transformer is straightforward engineering; doing it on ten thousand streets at once is a budget and a labour problem that no utility on the continent has solved.
So the throttling power in section 14a is best read not as a threat but as a confession of sequencing. The wires will be upgraded — the law assumes it — but not everywhere at once, and not before the heat pumps the federal government wants are meant to arrive. The dimming clause buys time. Whether households experience it as a fair trade or as a warm house held hostage will be one of the defining domestic-energy questions of the decade.
Berlin’s other route out of gas
What makes Berlin genuinely distinct is that it is not betting everything on the wire. For most of the city’s dense core, the answer to fossil heating was never going to be a heat pump bolted to each individual flat. It is the pipe already running beneath the road. Berlin has one of the largest district-heating networks in Western Europe — on the order of 2,000 kilometres of pipe, supplying heat and hot water to roughly 1.4 million residential units — and in 2024 the city took it back into public hands.
The deal had been signed with the Swedish utility Vattenfall in 2023; the Federal Cartel Office cleared it in early April 2024, and the sale closed soon after, for a sum reported in the region of €1.4 to €1.6 billion. The business that used to be Vattenfall Wärme Berlin now trades as Berlin Energie und Wärme — BEW — a company of the State of Berlin, with some 1,700 staff and a fleet of large heating and combined-heat-and-power plants. For the first time in a generation, the politics of how a million Berlin flats are warmed sits inside the Senate rather than across a negotiating table from it.
The point of owning it is to decarbonise it. Berlin intends to be off coal for heat by 2030 — the two coal-fired blocks at Reuter West are slated to wind down at the end of the decade — and to lift the renewable share of district heat substantially by 2030 on the way to a climate-neutral network. The chosen tools are revealing: large-scale heat pumps drawing warmth from treated sewage and rivers, heat storage, waste and industrial heat, biomass, geothermal. The same heat-pump physics, in other words — but applied centrally, where one big machine and one grid connection can do the work of thousands of small ones.
Two transitions, one substation
The honest reading of Berlin is that it is running two heating transitions at once, and they pull on the electricity system from opposite ends. In the dense districts, the district-heating network spares the low-voltage grid the worst of the load: a building on the pipe needs no nine-kilowatt compressor on its wall. In the outer, lower-density rings — the single-family houses of the city’s edge, where no pipe will ever reach — the heat pump is the only road, and that is precisely where section 14a’s dimming clause will be felt first.
This is not a contradiction so much as a division of labour, and it is the part most worth exporting. The temptation, in any city writing a heat plan, is to declare a single technology the winner. Berlin’s emerging answer is geographical: the pipe where the pipe makes sense, the pump where it does not, and a grid rule that lets the second category grow faster than the cables would otherwise allow. The municipal heat plan due in 2026 is, in effect, the document that draws that map — which addresses can expect district heat, and which are on their own with a compressor and a section-14a contract.
What the rating plate doesn’t say
Back on the Pankow side street, the electrician finishes the registration and the heat pump starts its first cycle, a low mechanical hum against the cold. The household has done everything the Heizungsgesetz asks. It has also, without quite intending to, become a node in a negotiation it cannot see — one of a growing number of devices whose demand the grid may have to choreograph on a hard winter night.
The numbers are not flattering to the original ambition. A 500,000-a-year target met by 193,000 installations is a gap that no amount of optimism closes quickly, and the BWP’s own forecast for 2025 — in the region of 260,000 units — still sits well below the line. But the more interesting story is not the shortfall. It is that the slowdown has bought the distribution grid a reprieve it badly needed, and that Berlin has used the breathing space to build a second, public route to warmth that does not depend on every cable in the city being replaced first.
Whether the rest of the European urban decade follows will depend less on the cleverness of the heat pump than on the patience of the institutions around it: a federal rule that lets the network throttle rather than fail, a city willing to own its pipes, and a heat plan honest enough to tell each street which transition it belongs to. The engineering, as ever, is the easy part.
Sources: Gebäudeenergiegesetz (GEG, amended version in force 1 January 2024) and Bundesministerium für Wohnen, Stadtentwicklung und Bauwesen; section 14a Energiewirtschaftsgesetz (EnWG) and Bundesnetzagentur rulings on steuerbare Verbrauchseinrichtungen; Bundesverband Wärmepumpe (BWP) and Bundesverband der Deutschen Heizungsindustrie (BDH) market figures for 2024–2025; Vattenfall and the Senate of Berlin on the 2024 sale of the district-heating business to the State of Berlin (now Berlin Energie und Wärme, BEW); Bundeskartellamt merger clearance, April 2024; Senatsverwaltung für Mobilität, Verkehr, Klimaschutz und Umwelt (Berlin) on the heat transition and coal exit by 2030.
